A large number of catalytic agents have been added to gasolines in an effort to increase combustion efficiency and ultimately reduce the production of unburned hydrocarbons, carbon monoxide, the oxides of nitrogen and other smog constituents. For example, boron compounds such as butyl borate and octyl borate are common fuel additives and, more recently, manganese compounds such as methyl cyclopentadienyl manganese tricarbonyl as described in U.S. Pat. No. 2,839,552 and other manganese compounds as described in a later U.S. Pat. No. 3,030,195 have been utilized to function as antiknock agents enabling the reduction of the tetraethyl lead. Quite recently, my own experimentations have indicated that certain particular combinations of boron and manganese additives provide a synergistic effect leading, for example, to the reduction of the oxides of nitrogen by as much as 40 percent according to results of tests by the California Air Resources Board. Theoretically, it would appear that such combination of catalytic agents reduces the activation temperature of carbon, thus allowing engines to run smoother with greater power, eliminate detonation, and reduce the output of smog. Careful observations of of the spark plugs used with such catalytic additive gasolines indicate initial condensing and subsequent eluting of the catalytic agents on the plug electrodes within the combustion zone of the engine.